1. Field of the Invention
The present invention generally relates to a method for forming an oxide film of a metal or silicon by plasma-assisted processing such as plasma-enhanced atomic layer deposition (PEALD).
2. Description of the Related Art
In a PEALD process, depending on the type of application, there are problems to be solved, such as oxidation of an underlying layer. Conventionally, this problem has been handled by lowering RF power. However, when RF power is lowered, desired properties of films such as thickness, uniformity, and wet etch rate, etc. cannot be obtained.
For example, low RF power is required in a SiO process where oxidation of an underlying layer 3 is undesired because, as illustrated in FIG. 1A when high RF power is applied, the underlying layer 3 is oxidized due to the effects of oxygen plasma, ion bombardment, and sputtering during film deposition. That is, when a SiO film 1 is deposited by PEALD on the underlying layer 3 in which W, TiN, or other materials are contained or which is a SiN film, the material constituting the underlying layer 3 is oxidized in an upper portion 2 thereof by a plasma including oxidizing gas used for deposition of the SiO film 1, and thereby desired device characteristics cannot be obtained.
Further, in hyperfine processing such as a process for an FinFET (a nonplanar, double-gate transistor built on an SOI substrate), as illustrated in FIG. 1B, a Si protrusion pattern 4 having a height of 6 nm is subjected to PEALD as shown in (a). When PEALD is performed under highly oxidizing conditions 7, the surface 5 of the protrusion pattern 4 is oxidized and eroded while a SiO film 6 is deposited by PEALD, thereby reducing the size of the protrusion pattern 4, particularly in a vertical direction (the height of the protrusion pattern 4 is reduced to 4 nm, for example) as shown in (b). As a result, the dimensions of the pattern are changed, and the deigned electronic properties may not be obtained. In contrast, when PEALD is performed under low oxidizing conditions 8, the surface of the protrusion pattern 4 is not significantly oxidized while a SiO film 6 is deposited by PEALD, thereby preventing a size reduction of the protrusion pattern 4, particularly in a vertical direction (the height of the protrusion pattern 4 can remain at 6 nm) as shown in (c).
In addition, low RF power is required in a process of film deposition on a photoresist because, as illustrated in FIG. 1C when high RF power is applied during the film deposition process, the photoresist dimensions are set back and reduced due to the effects of oxygen plasma, ion bombardment, and sputtering. That is, when an oxide 9 is deposited by PEALD on a patterned photoresist 10 formed on a substrate 11 in a double patterning process, a portion 12 of the underlying photoresist 10 is oxidized and eroded by a plasma including oxidizing gas used for deposition of the SiO film 9, and the desired dimensions of the photoresist 10 cannot be obtained.
Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion were known at the time the invention was made.